The present invention relates to a magnetic recording/reproducing apparatus of the helical scan type such as a video tape recorder (a VTR), a video cassette recorder (a VCR), or the like.
Color television signals encoded in a standard NTSC manner or in a standard
manner include luminance components and chrominance components quadrature-modulated into a color subcarrier. When these signals are recorded on a magnetic tape by a magnetic recording/reproducing apparatus, generally, a "color under" system is used.
In this system, the color subcarrier, quadrature modulated with chroma components, is directly recorded at a low frequency on the same tape track with an FM carrier modulated by video luminance information. To improve linearity, the directly recorded chrominance information is recorded with the aid of a bias signal. To prevent interaction between the bias signal and the frequency-modulated carrier, the FM carrier is often used as the bias signal.
In a "VHS" system known as a "VTR" system for home use, the frequency of a subcarrier of recorded chrominance information is selected to be 0.629 MHz, and the frequency of an FM carrier is, on the other hand, selected to be 3.4 MHz-4.4 MHz.
While such an arrangement allows recording of a color television signal on a single track of a video tape recorder, certain problems exist, such as poor SN of the chrominance signal, crosstalk between the two quadrature-modulated color signals, and limited frequency bandwidth which necessitates reduction of the desired bandwidth in either the chrominance or luminance information, or possibly both. Furthermore, the FM luminance carrier cannot be modulated to the maximum possible amount because maximum modulation drives the recording medium into saturation, adding distortion to the directly recorded chrominance information.
In order to improve the quality of the television signal to broadcast standards, the luminance information may be recorded on a first track of the tape by the use of a frequency-modulated carrier, while at the same time recording the chrominance information onto a second track of the tape adjacent the first. The chrominance information is modulated onto a frequency-modulated carrier for improved signal-to-noise.
The "two-channel" VTR of the type as described above is disclosed, for example, in U.S. Pat. No. 4,376,957.
It is a matter of course that the information recorded in the foregoing VTR of the "VHS" system is different in format from the information recorded in the foregoing "two-channel" VTR. Therefore, the conventionally known VTR of the "VHS" system cannot reproduce information signals recorded by the "two-channel" VTR, while the "two-channel" VTR cannot reproduce information signals recorded by the VTR of the "VHS" system.
Generally, the VTR of the "VHS" system is provided with two operation modes, one being called an "SP" mode and the other an "EP" mode. In the "SP" mode, a magnetic tape is fed at a speed of about 33 mm/sec, and a pitch of a recording tack is selected to be 58 .mu.m. In the "EP" mode, on the other hand, a magnetic tape is fed at a speed of about 11 mm/sec, and a pitch of a recording track is selected to be 19 .mu.m. The "EP" mode is also called a "triple" mode. In the helical scan type VTR generally provided with two rotary magnetic heads being different in azimuth angle from each other and being disposed on a rotary head drum separately from each other by an angle of 180 degrees, a video signal for one frame, that is, two fields, is recorded on a magnetic tape by the two heads alternately for the respective fields one by one. The foregoing VTR of the "VHS" system is provided with two video heads for the "SP" mode and two video heads for the "EP" mode. Further, known is a VTR of the "VHS" system provided with two rotary sound heads in addition to the four video heads. A frequency-modulated sound signal is recorded by these sound heads onto a track having the same inclination as a track on which a video signal is to be recorded, that is, the video signal is written in a tape so as to be superimposed on the sound signal. The sound signal is recorded in a deep position of the tape while the video signal is recorded in a shallow position of the same. The two sound heads are different in azimuth angle from each other, and further the respective azimuth angles of the two sound heads are different from those of the video heads. The width of a track on which a sound signal is recorded is selected to be about 20-25 .mu.m. Thus, the number of magnetic heads is six in the VTR of the "VHS" system having rotary sound heads.
In the "VHS" system, a frequency-modulated sound signal to be recorded in a deep portion and a video signal to be written so as to be superimposed on the former are required to satisfy the following conditions. These conditions are determined so as to reduce a crosstalk as well as a timing error between the video and sound signals.
That is, in the "SP" mode, the video and sound signals are recorded with azimuth angles in the opposite direction to each other and a time deviation of the video signal from the sound signal is selected to be within two fields. In the "EP" mode on the other hand, the video and sound signals are recorded with azimuth angles in the same direction with each other, and the time deviation therebetween is selected to be within a range from 11/3-31/3 fields.
Such a "VHS" system as described above is disclosed in detail, for example, in U.S. Pat. No. 4,591,924.
Recently, an apparatus capable of recording/reproducing video signals of both the "color under" system and the "two-channel" system has been required. If the VTR of the "two-channel" system is incorporated in the VTR of the "color under" system, the foregoing apparatus may be realized. However, if both the VTRs are assembled merely integrally with each other, many magnetic heads must be required because it is necessary to provide two pairs of magnetic heads in the "two-channel" VTR.
Further, no compatibility exists between the "two-channel" VTR and the VTR of the "VHS" system. Further, either in the "SP" mode or in "EP" mode, no compatibility exists between both the VTRs.